Styrofoam prepared by foaming expandable polystyrene beads is often used as a raw material for a disposable product, but is being magnified as a main cause of environmental pollution because in the case of discharging it after using Styrofoam to natural environment, it is not discomposed, and thus semi-permanently left. Therefore, the researches on a biodegradable material for replacing Styrofoam are being actively carried out, but a material capable of totally replacing Styrofoam is as yet undeveloped.
Starch is often used as a main component for a biodegradable material capable of replacing Styrofoam, and U.S. Pat. No. 4,863,655 discloses a method for preparing a biodegradable buffer material, in which the method includes supplying starch or modified starch, and water as a foaming agent to an extruder and then foam-molding. However, in the case of foam-molding using an extruder, it is difficult to prepare foams having various shapes and sizes, and foam in a type of peanut is mainly prepared. In addition, in the case of foams prepared by using general starch as a main component, there are limitations on the replacement of Styrofoam as for physical properties, and the like. In addition, there is a case of preparing foams, in which starch is foamed by using an extruder, and then the foamed extrudate is subjected to a complex working process, such as a compression, junction, and cutting to give a type. However, equipment of foaming expandable polystyrene beads cannot be used, and also there are limitations on a use and economic feasibility due to a multi-step process. In addition, US Patent Publication No. 2007/0021515 discloses a method for preparing foams having a specific type, in which the method includes extruding a starch composition including starch, and a foaming agent such as water or alcohol by an extruder to prepare beads, and then foam-molding the prepared beads to give a specific type. However, there are problems such that a type of a usable foaming agent is limited because of properties of starch, so that special foaming equipment is required instead of equipment for foaming expandable polystyrene beads, which uses various molds and steam when preparing foams, and there are limitations on a rate of foaming, and the like.
Meanwhile, the researches on a production of foams or expandable beads using a biodegradable resin, such as polybutylene succinate and polylactic acid are constantly being carried out, and development cases are reported. However, it is expensive as compared with expandable polystyrene beads, and has a poor mechanical property as compared with Styrofoam, so that there are limitations on a use of it.